1. Field of the Invention
The present invention relates to a method for manufacturing a white light emitting diode, and more particularly to a method for producing a molding compound resin tablet for wavelength conversion which is capable of ensuring uniform distribution of a phosphor and a method for manufacturing a white light emitting diode by using the production method.
2. Description of the Related Art
Generally, since light emitting diodes (LEDs) have advantages in terms of monochromatic peak wavelengths, a high light efficiency and a small size, light efficiency and miniaturization, they have been widely used as display devices and light sources. Among these LEDs, white light emitting diodes are progressively utilized as high output and high efficiency light sources which can replace backlights of illuminators or display devices.
Such white light emitting diodes are predominantly manufactured by a wavelength conversion process wherein a phosphor is applied onto a blue or UV light emitting diode to convert the blue or UV light to white light.
FIG. 1 is a cross-sectional view of a white light emitting diode package 10 fabricated in accordance with a conventional method.
Referring to FIG. 1, the white light emitting diode package 10 comprises two lead frames 3 and 4, a blue light emitting diode 5 mounted on a cap 3a of the lead frame 3, and a transparent molding portion 8 formed on the lead frames 3 and 4. Both electrodes of the blue light emitting diode 5 are electrically connected to wires 6 and 7, which are connected to lead frames 3 and 4, respectively.
A resin 9 including a Y—Al—Ga (YAG)-based phosphor is molded inside the cap 3a formed on the lead frames 4 so as to surround the blue LED 5. The blue LED 5 emitting blue light can produce the desired white light by combining a portion of light excited into yellowish green light having a peak wavelength of 555 nm and a portion of blue light directly emitted from the LED.
Commonly, the resin 9 containing the phosphor is formed on the LED 5 by a dispensing process using a liquid resin.
However, the dispensing process is not suitable for mass-production when compared to other molding processes. In addition, since the dispensing process uses a liquid resin, phosphor particles may be precipitated in the liquid resin during curing of the liquid resin. The precipitation of the phosphor particles causes non-uniform dispersion in the resin layer 9 surrounding the LED 5. The light converted from the resin layer 9 in which the phosphor is non-uniformly dispersed partially exhibits a yellowish white or bluish white color, resulting in non-uniformity in color.
In order to solve the above-mentioned problems of the prior art, a white light emitting diode manufactured by a transfer molding process is proposed in Korean Patent No. 348377, which was issued on Jul. 9, 2002. According to this patent, as shown in FIG. 2, the white light emitting diode is manufactured by a method comprising the steps of mixing a phosphor powder with a molding compound resin powder, e.g., an epoxy molding compound powder (step S21), shaping the mixture into a molding compound resin tablet (step S25), and transfer-molding a blue light emitting diode using the tablet (step S29) to manufacture the desired white light emitting diode.
Since the method employs a transfer molding process having a relatively short curing time, it has advantages that deterioration in the light conversion efficiency due to the precipitation of phosphor particles can be prevented, and at the same time, the mass-production of the white light emitting diode can be enhanced.
However, since the phosphor powder and the molding compound resin powder having different specific gravities and particle sizes are mixed with each other to produce the molding compound resin tablet, it is difficult to realize uniform distribution of the phosphor powder in the tablet.
Despite the advantages of the transfer molding process, the white light emitting diode thus manufactured still emits yellowish white or bluish white light, and thus it is difficult to manufacture a light emitting diode having a high light conversion efficiency.